The U.S. Pat. No. 4,859,000 shows an adaptive brake control with an electropneumatic engineman's brake valve and a relay valve. In the flow connection between the relay valve and a main air pipe (called HL hereinafter) there are three sensors, which measure the flow rate, the absolute pressure and the temperature of the air. Other pressure transducers at the engineman's brake valve measure the pressure of a control pressure container for the relay valve (A pressure) and the pressure in the engineman's brake valve for the requested brake pressure. The output signals of all of these sensors are fed to a microprocessor and evaluated. Primarily the volume of air flowing into the HL by way of the relay valve when the brakes are released or the volume of air flowing out of the HL by way of the relay valve during the braking process is measured.
When a new train is assembled, starting from a totally vented HL, the volume of the supplied air up to the total release of the train is measured and the value is stored. When the HL is later totally vented, a comparison is made as to whether the same volume flowed out. Inversely, it can also be determined later with this comparative value, whether the brakes were completely released. With each braking and releasing manoeuvre, the volume flowing out of the HL during the braking process is always compared with the volume flowing into the HL during the braking process, from which comparative value the changes in the train configuration (e.g. foreseeable closing of a shutoff valve on a wagon) or other failures can be detected. Furthermore, this document deals in detail with the problem of a renewed braking at a time at which the brakes are not yet completely released, thus air is still being backfed into the HL. In such a case the control pressure container (A container) is already filled up to the pressure for the new braking demand signal, whereas the pressure in the HL is still below this value. By braking again in the release phase, the pressure in the A container is reduced relatively rapidly in accordance with the selected brake step. The control valves of the individual wagons respond to the pressure differential between the current pressure in the A container and the HL pipe, a feature that leads to no braking or only to a braking with a smaller brake step than that selected. To solve this problem, in this publication the value of the pressure in the A container is stored at a time at which the flow rate of the backfed air into the HL goes towards zero. At this time the pressures in the A container and the HL are about equal. For the subsequent braking process the value of the pressure in the A container is corrected in accordance with the difference between the closed loop control pressure in the A container and the stored value. For the subsequent braking process one starts then with less A pressure so that the effective pressure drop in the HL that is necessary for the braking process corresponds to the demanded brake step.
This known system assumes that in the individual wagons no air is consumed, rather the volume of air flowing out of the HL during the braking process is always equal to the volume of air required to subsequently totally release said brake. This requirement, however, is not met for brake systems produced in conformity with the UIC standard, since the air flowing during the braking process out of the air supply containers (R containers hereinafter) in the individual wagons to the brake cylinders does not flow back any more into the R containers or the HL when the brakes are released but rather is vented to the open air. Thus, each brake and release cycle results in a consumption of air. This air consumption depends on the length of the train (number of brake cylinders), the chosen brake step, eventual leakiness of the brake system and indirectly also on the weight of the train. Changes in the length of the train by coupling and uncoupling the wagons can only be properly considered, if the train in the new configuration is totally bled (braked) and then released again. In the known system small leaks of HL, which can be accepted in accordance with UIC standard without further ado, would lead to error messages or even to malfunctions.
In the DE journal ETR 37 (1988), issue Jan. 2, pp. 37-43, an electronic brake control for rail vehicles is described, in which control a differential pressure sensor is used to determine the the mass or volume flow of the air flowing into the HL. To release the brakes faster, the HL-pressure setpoint is specifically increased as a function of the preceding braking process, the response time of the valves and the course of the backfeed. The current setpoint of A pressure at the first wagon is the result of the setpoint of the HL pressure corrected by a value that considers the pressure drop between the measuring point and the control valve in the first wagon during the instantaneous rate of air flow in the HL.
A similar engineman's brake valve is described in the EP-A-0.152. 958. There a flow sensor in the form of a differential pressure gauge is provided in the backfeed pipe (HB pipe) and a pressure gauge in the HL. A setpoint signal for the pilot control pressure is corrected on the basis of these measured values, with which the HL pressure can be transformed to the pressure at the first control valve of the first wagon. In this manner the HL pressure is increased as a function of the length of the pipe; and the length of the filling stroke is adjusted to the length of the pipe. This adaptation, however, is still quite inaccurate.